Interface Characterization

The spectra of the ultrathin PMMA on aluminum oxide substrates were acquired on an ambient pressure X-ray photoelectron spectrometer (SPECS Phoibos 150 NAP). Time between the deposition of the PMMA films and the introduction of the samples in the analysis chamber was kept as small as possible. At room temperature, ambient gas (oxygen, nitrogen, carbon dioxide, …) is dissolved in liquid water. Since it is desired to only dose water molecules in the analysis chamber, water (18.2 M Ω cm) was degassed by three cycles of liquid nitrogen freeze-pump-thaw before introduction into the APXPS analysis chamber from a glass vessel via a precision leak valve. A pass energy of 20 eV and an energy step of 0.05 eV were used to record the spectra of the different photoelectron core levels. The X-ray source (Al K-alpha, monochromatized, SPECS MF 60) was set at an acceleration voltage of 14 kV and a power of 100 W was used for the irradiation of the organic/inorganic system. The fitting procedure was performed by utilizing KolXPD software. Peak shapes consisted of a Voigt mixture of Gaussian/Lorentzian, with a Shirley type background. The binding energy scale was calibrated by setting the aliphatic (C−C/C−H) component of the C 1 s peak to 284.8 eV after fitting.

Infrared spectra were recorded with a Thermo-Nicolet Nexus Fourier transform infrared spectroscopy (FTIR) apparatus equipped with a mercury-cadmium-telluride (MCT) liquid-nitrogen-cooled detector, and a nitrogen-purged measurement chamber with a Harrick Seagull multipurpose reflection accessory. The resolution of the acquired spectra is 8 cm⁻¹. The control of the spectra acquisition was managed by the OMNIC 8.1 software package (ThermoElectron Corporation, Madison, WI). A spectrum of the IRE crystal coated with aluminum oxide against pure toluene was taken as a background prior to the polymer deposition and polymer solution exposure. For the water ingress measurements, a spectrum of the IRE crystal coated with aluminum oxide against ambient conditions was taken as a background prior to polymer deposition and prior to electrolyte exposure.

ToF-SIMS measurements were performed using a TOF.SIMS 5 (ION-TOF GmbH). Static SIMS conditions with a total ion dose less than 1 × 10¹³ ions cm ⁻² analysis ⁻¹ were employed using a 30 kV Bi3+ primary ion beam operating in the high current bunched mode for high spectral resolution. An analysis area of 100 × 100 μm ² at a resolution of 128 × 128 pixels was used. ToF-SIMS spectra were acquired over a mass range of 1–850u in both positive and negative ion modes. Fragments of known composition, such as CH3+, C2H2+, AlOH⁺, C⁻, CH2+, C₂H₃O⁻ and AlO⁻ were used for mass calibration and carefully checked to confirm that these peak shapes did not show any charging effect.